Method and apparatus for magnetic forming

ABSTRACT

A method and apparatus are described for magnetically forming a workpiece. A magnetic field is repetitively produced, the field being of a size for forming the workpiece in a subregion which is substantially smaller than the total region to be formed. The workpiece and the means producing the magnetic field are displaced relatively an amount which provides full coverage of the total region to be formed after a series of repetitions of the magnetic field.

United States Patent Inventor Paul Wildi San Diego, Calif. Appl. No. 812,129 Filed Apr. 1, 1969 Patented June 1, 1971 Assignee Gulf Energy & Environmental Systems,

Inc. San Diego, Calif.

METHOD AND APPARATUS FOR MAGNETIC FORMING 9 Claims, 10 Drawing Figs.

US. 01 72/56, 72/80, 72/706 Int. Cl B21d 26/14 Field 61 Search 72/706, 56, 80; 29/421 [56] References Cited UNlTED STATES PATENTS 3.149372 9/1964 Stinger 29 421 3,203,211 8/1965 Mallinckrodt .1 72/56 3,212,311 10/1965 lnoue 72/56 3,288,006 11/1966 Erlandson 72/56 3,314,260 4/1967 Habdas et al. 72/56 3,360,972 l/1968 Schwinghamer et al 72/56 3,365,522 l/l 968 lnoue 72/56 Primary Examiner-Richard J. Herbst Attorney-Anderson, Luedeka, Fitch, Even and Tabin ABSTRACT: A method and apparatus are described for magnetically forming a workpiece. A magnetic field is repetitively produced, the field being of a size for forming the workpiece in a subregion which is substantially smaller than the total region to be formed. The workpiece and the means producing the magnetic field are displaced relatively an amount which provides full coverage of the total region to be formed after a series of repetitions of the magnetic field.

ENERGY PULSE PATENT ED JUN 1 I97! SHEET 1 BF 3 FlG.l

MOTOR SPEED CONTROL INVENTOR PAUL WILD! PATENTED JUN Hen 3,581,541

SHEET 3 [IF 3 FIG.9

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"5 III INVENTOR PAUL WILDI ATTYS.

METHOD AND APPARATUS FOR MAGNETIC FORMING This invention relates to magnetic forming and, more particularly, to an improved method and apparatus for magnetically forming a workpiece.

It is well known to form material by employing transient magnetic fields of high intensity. An example of apparatus for accomplishing this is shown and described in the US. PAT. No. 2,976,907, issued Mar. 21, I96l, and assigned to the assignee of the present invention. In apparatus generally of this type, an electrical current pulse of high amperage is passed through a conductive coil, thereby producing a transient mag netic field of high intensity. A conductive workpiece positioned in the transient magnetic field has a current induced in it corresponding to the changing flux of the transient magnetic field. The induced current pulse interacts with the magnetic field to produce a force acting on the workpiece. If the force is sufficiently strong, a deformation of the workpiece results. The shape of the deformation is dependent upon the shape of the magnetic field and the position of the workpiece relative to the field. Repeated pulses of current may be supplied to the conductive coil, thus causing a series of forming pulses to be applied to the workpiece.

Ordinarily, greater force concentration then can bc obtained from a conductive coil alone is provided by employing a magnetic field shaper as part of the coil structure. One form of field shaper is that of a conductive body, such as a conductive plate having an aperture therein for accommodating the workpiece. The area of the aperture is ordinarily smaller than the area enclosed by the coil. The field shaper is disposed relative to the coil such that the transient magnetic field produced by the coil induces a transient current in the field shaper which is concentrated on its inner surface around the aperture, and creates an intense field in the aperture. The flux density within the aperture and, therefore, the force on the workpiece, are dependent upon the shape of the inner surface of the field shaper at the aperture and upon the location of the inner surface relative to the workpiece. For example, a tube can be constricted intermediate its ends through the use of a field shaper which includes an annular flange projecting inwardly from the inner surface of the field shaper to define a narrow throat within the aperture.

Where the total region to be formed on a workpiece is of substantial size, some problems may be encountered. This is because, due to the relatively large surface of the workpiece, very considerable magnetic energies are involved. This may be true even though a comparatively low forming pressure is required. As a consequence of the high level of magnetic energy required, the capital cost of magnetic forming equipment is correspondingly increased. Thus, for many types of workpieces wherein large regions are to be formed, known techniques of magnetic forming may be impractical due to their high cost.

Another problem encountered in connection with the formation of relatively large regions or areas on workpieces is related to the efficient use of electrical energy. During magnetic forming, the magnetic flux is essentially confined between the coil structure and the workpiece. Where the workpiece is of substantially uniform wall thickness and, consequently, the forming to be done is of approximately the same severity over the whole area or region to be formed, it is desirable to have approximately uniform pressure over this region or area. Accordingly, the magnetic flux density should be maintained substantially uniform throughout the gap between the coil structure and the workpiece. In order to do this where the annular gap between the workpiece and the coil varies in diameter, the gap width must also be varied. The smaller the diameter of the annular gap, the larger the gap width should be to maintain constant flux density. Limitations exist, however, on how small the gap width may be made due to considerations of workpiece size variation, clearance, and the need for electrical insulation. For this reason, the gap width associated with the smallest gap diameter may be so large as to require the expenditure of considerable excess energy, since the energy required is directly related to the volume defined by the gap over the whole coil.

Certain workpiece configurations may present problems in designing a coil structure to effect the desired deformation. As mentioned above, problems in connection with the size of the area to be deformed, and in connection with the necessity for excessively large coil structureworlcpiece gaps to maintain uniform flux density, arise in connection with certain workpiece shapes. Moreover, it may be difficult or impossible to design a coil structure to effect a desired deformation. For example, where the workpiece is generally dome-shaped, previously known designs of magnetic forming apparatus have been unable to form the dome-shaped region in an efficient manner.

It is an object of the present invention to provide an improved method and apparatus for magnetically forming a workpiece.

Another object of the invention is to provide a method and apparatus for magnetically forming, at low cost, relatively large regions on workpieces.

A further object of the invention is to provide a method and apparatus for magnetically forming workpieces which is adapt-able to a wide variety of shapes of workpieces and of shapes of regions thereon to be formed.

Other objects of the invention will become apparent to those skilled in the art from the foregoing description, taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic perspective view of apparatus constructed in accordance with the invention for performing the method of the invention;

FIGS. 2-5 illustrate variations in the shape and the positioning of the coil structure used in the apparatus of FIG. 1;

FIG. 6 is a plan view of a further embodiment of the invention;

FIG. 7 is an elevational view of the embodiment of FIG. 6;

FIG. 8 is a plan view of still another embodiment of the invention; and

FIGS. 9 and 10 are sectional schematic views illustrating, respectively, two further embodiments of the invention.

Very generally, the method of the invention comprises repetitively producing a magnetic field of a size for forming the workpiece in a subregion to be formed. Relative displacement is effected between the workpiece and the means producing the magnetic field an amount which provides full coverage of the total region to be formed after a series of repetitions of the magnetic field.

The method of the invention will be best understood by reference to FIG. I in connection with a specific type of work piece. The workpiece comprises a dome-shaped light reflector l l, on the surface of which a diamond pattern is to be formed. Typically, such light reflectors are fabricated by first spinning them into a circular shape and then forming them over an inside die 12. The outer surface of the die is configured in the desired diamond patter, and, when a reflector is compressed against the die, the diamond pattern is formed on the surface of the reflector. It may be noted that the rim of the reflector surrounding its open end is provided with an outward flange 13 which is formed to provide an annular recess.

In order to form or swage the reflector 11 against the die 12 to form the desired diamond pattern, the technique of magnetic forming may be utilized. A magnetic forming coil structure, including a field shaper if utilized, is generally of annular configuration. In order to apply magnetic pressure across the entire outer surface of the region to be formed on the workpiece 11, the inner surface of the coil. structure may be configured to mate with that of the outer surface. In doing this, however, the change in diameter due to the contour of the dome introduces inefficient gap widths as described above. Thus, a magnetic forming coil structure of a height equal to the region to be formed and of an inner diameter which varies with the contour of the reflector is inefficient and requires a very large source of energy, increasing the capital cost of the equipment.

The method of the invention avoids the necessity for very large forming coil structures conforming with the full contour of the region to be formed. In accordance with the method of invention, a smaller forming coil structure requiring a smaller energy source is designed to form an area which constitutes an increment of the entire region to be formed. Since magnetic forming equipment is particularly adapted for repeated pulsing (for example an energy pulse every 6 seconds) the smaller area can be moved around or across the entire surface or region to be formed by effecting relative movement between the workpiece and the forming coil structure. By effecting such relative movement, and by proper selection of the configuration of the forming coil structure, full coverage of the total region to be formed may be achieved after a series of repetitions of the energy pulse producing the magnetic field. The relative movement is preferably synchronized with the repetitions of the magnetic field to provide a sufficient overlap between the adjacent subregions or smaller regions of each pulse. This ensures even forming throughout the total formed reg|on.

In FIG. 1, apparatus for accomplishing the method of invention is illustrated. The apparatus includes a coil structure 16 which is annular and which is disposed with its axis oblique to the axis of the dome-shaped reflector 11. The innermost surface 17 of the coil structure 16 is formed to provide a uniform gap between the coil structure and the workpiece or reflector. The exact details of the construction of the forming coil structure 16 are not illustrated, but it is to be understood that the preferred type of coil structure is comprised of a plurality of closely spaced individual turns embedded in a suitable insulation, such as epoxy. Current is conducted to and from the coil structure 16 by a suitable pair of conductors 18 and 19, illustrated schematically in the drawing. The coil structure 16 is supported at the illustrated position by a suitable structure, illustrated schematically as the plate 21. The specific techniques for providing a coil structure mounted as shown are well known in the art, and are therefore not disclosed herein in detail.

The conductors 18 and 19 are connected to a suitable energy pulse source 22, such as a bank of capacitors. The energy pulse source provides pulses of electrical energy to the coil structure 16 for establishing the magnetic field as previously described. The region which is deformed by a single pulse with the workpiece and the coil structure in the relative positions shown is the region 23 between the dotted lines. The region 23 corresponds generally to the facing surface 17 of the coil structure.

In performing the method of the invention, the workpiece or dome 11 is rotated on its own axis relative to the coil structure 16. Accordingly, repeated pulsing of the coil structure 16 will cause forming of the workpiece in regions which are identically shaped to the region 23, but which are displaced therefrom. Depending upon the timing of the pulses and the rotation of the workpiece, the smaller deformations produced upon each pulse may be made contiguous or overlapping, eventually completely forming the workpiece in the region between the dash-dot lines 24. In the illustrated embodiment, this produces the desired diamond-shaped pattern on the interior surface of the workpiece in that region.

In order to effect rotation of the workpiece 11 about its axis and with respect to the coil structure 16, the workpiece and inside die 12 are supported on the top of a turntable 26. The die is located on the turntable with the turntable and the die being in axial alignment, and the lower edge of the die is provided with an annular shoulder 27 which mates with the annular recess formed by the flange 13 on the domed reflector 11. This locates the dome with respect to the coil structure 16 and to the turntable.

The turntable 26 is supported on a rotary shaft 28, The shaft 28 is rotated in the direction of the arrow 29 by a motor 31. Provision is also made for moving the shaft 28 reciprocally along its axis in the direction of the arrows 32. Preferably, such provision is incorporated in the design of the motor 31.

Suitable alternative means, however, may be employed. By moving the shaft 28 axially, the workpiece 11 may be removed from within the coil structure 16 to facilitate removing the workpiece from the die 12. The speed of the motor 31 and hence the speed of rotation of the workpiece 11 is controlled by a motor speed control 33 of any suitable design. As indicated by the dotted line 34, the speed control 33 and the energy pulse source 22 may be synchronized to provide pulses with the desired degree of overlap between adjacent subregions as to ensure even forming throughout the total formed region between the dot-dash lines 24.

Since the size of the region formed by each pulse is substantially less than that if the entire region were formed at once, the size of the energy pulse source 22 may be correspondingly smaller. The necessity for repetitive pulses presents no problem, since magnetic forming apparatus is inherently capable of being fired in short intervals. Efficiency is maintained at a high level since the necessity for variation in gap width between the coil structure and the workpiece is minimal.

An additional advantage of this method is that the forming can be extended to the apex of the dome. This is not possible with a coil structure which forms the entire region at once. Even a coil of many turns formed in a frustoconical helix would have a region of zero pressure at the apex. In accordance with the invention, forming is extended to the apex of the dome by positioning the coil structure 16 as illustrated in FIG. 2. The coil extends over the apex 14 of the domelike workpiece and, when the workpiece is rotated about its axis relative to the coil structure, forming occurs in the entire region above the dash-dot line 24.

In FIG. 3, a further variation on the shape of the coil structure 16 is illustrated. The coil structure, although still a loop or closed on itself, is of noncircular outline. By varying the shape of the coil in this manner it is possible to create more intense forming in some zones of the workpiece than in others. This may be desirable in certain applications.

In FIG. 4, an arrangement is shown wherein the coil structure 16 does not surround the apex 14 of the domelike workpiece 11. In this case, although the axis of the coil structure 16 is oblique to the axis of the workpiece, the axis of the workpiece extends outside of the periphery of the coil structure. In some instances, depending upon the material, the particular type of formation required, and other factors, an arrangement such as that shown in FIG. 4 may be desirable.

A further variation of the embodiment of FIG. 1 is illustrated in FIG. 5. In this variation, the coil structure 16 has been shaped to make the current return density in the wider leg of the coil minimal. Moreover, the legs of the coil extending meridionally to the domelike workpiece 11, are substantially linear, thereby applying pressure over a substantially linear area. This latter configuration may be of advantage in forming a series of meridional grooves in the workpiece.

Referring now to FIGS. 6 and 7, a further embodiment of the invention is illustrated. In the embodiment of FIGS. 6 and 7, the workpiece to be formed is a generally flat disc 111, supported on a die 112, the upper surface of which is machined with a desired pattern to be embossed on the underside of the disc 111. The die 112 and the disc 111 are supported on a turntable 126 which is rotated on a shaft 128 in the direction of an arrow 129, as previously explained in connection with the embodiment of FIGS. 1-5.

Although the workpiece 1 11 could be formed by means of a flat spiral coil, the high energy requirements of such a coil, and the lack of deforming force at the center thereof, may make it undesirable in certain circumstances. In accordance with the invention, a loop coil structure 116, of suitable construction, is supported by means not illustrated just above the workpiece 111. The axis of the coil is parallel to the axis of the workpiece turntable, but is displaced therefrom. As the workpiece 111 is rotated on the turntable 126, the coil structure 116 is repetitively energized, as previously explained, to produce a succession of contiguous deformations in the workpiece and thus deform the entire region desired after a series of repetitive energizations and appropriate relative rotations. The size and shape of the coil structure 116 may be selected to be appropriate to the deformation desired, as previously discussed in'connection with FIGS. l-5.

A principle generally analogous to that illustrated in FIGS. 6 and 7 is employed in the embodiment of FIG. 8. In FIG. 8, the invention is employed in the working of a continuous strip workpiece 211, in the manner of a rolling mill, the strip being moved under a stationary coil structure 216. The invention as illustrated in the embodiment of FIG. 8 may, for example, be used for the embossing of a strip with decorative patterns. The die, not shown, which is under the strip 211, would consist ofa roll, or several rolls, or it would have to be self-releasing in order not to lock the strip after each working pulse.

In the previous embodiments illustrated and discussed herein, the working force has been exerted either radially inward with respect to the annular coil structure, or normal to theplane of the coil structure, or a combination of these. in FIG. 9, deformation of a tubular workpiece 31] in a radially outward direction is illustrated. The annular coil structure 316 is suitably supported, by means not illustrated, interiorly of the tubular workpiece, and the tubular workpiece is moved in the direction of the arrow relative to the coil structure. By energization of the coil structure magnetic pressure is produced between the outer periphery of the coil structure and the inner surface of the tubular workpiece. Each pulse of the coil structure produces an annular outward deformation in the workpiece, and as the workpiece is moved axially, these annular deformations can be made to overlap, to thereby produce an overall continuous expanded region.

Another variation in the invention is illustrated in FlG. 10. The embodiment illustrated in PK]. 10 is for producing an inward deformation of a tubular workpiece 411 by means of an annular coil structure 416, suitably supported to surround the workpiece. The coil structure is tilted so that its axis intersects the axis of the workpiece obliquely. As the workpiece is rotated in the direction of the arrow 429, by suitable means not illustrated, repetitive energization of the coil structure 416 will produce a formed region, after a series of pulses, between the dash-dot lines 424. Thus, a smaller coil structure may be utilized to effect the forming with the advantages regarding power requirements previously mentioned.

Although the examples discussed herein have a stationary coil structure and a movable workpiece, it is to be understood that the same relative motion between the coil structure and movable workpiece may be obtained if the workpiece is stationary and the coil structure is movable, In addition, both the coil structure and the workpiece may be made movable.

It may therefore be seen that the invention provides an improved method and apparatus for magnetically fonning a workpiece. The method and apparatus are particularly adapted for forming relatively large regions in a workpiece at lower cost than that required in connection with the use of very large coil structures. The method and apparatus of the invention are adaptable to a wide variety of shapes of workpieces and shapes of regions thereon to be formed. The invention effects a substantial reduction in capital cost of the equipment, and provides a means of handling large objects which might otherwise be beyond the capability of on-hand ap paratus.

Various modifications of the invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

What I claim is:

1. Apparatus for magnetically forming a workpiece which is symmetrical about an axis, comprising, a generally annular coil structure for producing a magnetic field ofa size for forming a workpiece in a subregion which is substantially smaller than the total region to be formed, means for repetitively energizing said coil structure, said coil structure being oriented such that its axis is noncoaxial with respect to the axis of the workpiece, and meansfor effecting relative rotational movement between said COli structure and the workpiece on the axis of the workpiece.

2. Apparatus according to claim 1 for forming a workpiece of generally disc shape wherein said annular coil structure is supported with its axis perpendicular to the workpiece, and wherein said movement effecting means produce relative rota tional movement between said coil structure and the workpiece on an axis parallel to and displaced from the axis of said coil structure.

3. Apparatus according to claim 1 wherein said coil structure is supported with its axis oblique to the axis of the workpiece.

4. Apparatus according to claim 3 wherein the axis of the workpiece lies within the inner perimeter of said coil structure.

5. Apparatus according to claim 3 wherein the axis of the workpiece intersects said coil structure.

6. Apparatus according to claim 3 wherein the axis of the workpiece lies outside the outer perimeter of said coil structure.

7. Apparatus according to claim 3 wherein said coil structure is noncircular to create zones of more intense magnetic pressure on the workpiece.

8. Apparatus according to claim 3 wherein said coil structure is provided with at least two portions of substantially different cross section to create zones of correspondingly different magnetic pressure.

9. Apparatus according to claim 3 for forming a domeshaped workpiece wherein said coil structure is supported to extend over the apex of the workpiece. 

1. Apparatus for magnetically forming a workpiece which is symmetrical about an axis, comprising, a generally annular coil structure for producing a magnetic field of a size for forming a workpiece in a subregion which is substantially smaller than the total region to be formed, means for repetitively energizing said coil structure, said coil structure being oriented such that its axis is noncoaxial with respect to the axis of the workpiece, and means for effecting relative rotational movement between said coil structure and the workpiece on the axis of the workpiece.
 2. Apparatus according to claim 1 for forming a workpiece of generally disc shape wherein said annular coil structure is supported with its axis perpendicular to the workpiece, and wherein said movement effecting means produce relative rotational movement between said coil structure and the workpiece on an axis parallel to and displaced from the axis of said coil structure.
 3. Apparatus according to claim 1 wherein said coil structure is supported with its axis oblique to the axis of the workpiece.
 4. Apparatus according to claim 3 wherein the axis of the workpiece lies within the inner perimeter of said coil structure.
 5. Apparatus according to claim 3 wherein the axis of the workpiece intersects said coil structure.
 6. Apparatus according to claim 3 wherein the axis of the workpiece lies outside the outer perimeter of said coil structure.
 7. Apparatus according to claim 3 wherein said coil structure is noncircular to create zones of more intense magnetic pressure on the workpiece.
 8. Apparatus according to claim 3 wherein said coil structure is provided with at least two portions of substantially different cross section to create zones of correspondingly different magnetic pressure.
 9. Apparatus according to claim 3 for forming a dome-shaped workpiece wherein said coil structure is supported to extend over the apex of the workpiece. 